Seeking clarification about using OpenEXR headers

Hi,

This has annoyed me at various points in the past, but since it showed 
up again for me today, I thought I would seek clarification.

I have been assuming the the intended way for including OpenEXR headers 
was using this form:

#include <ImfInputFile.h>

Certainly, that is how the examples that come with OpenEXR include the 
headers.

However, I do see source code out in the wild that uses this form instead:

#include <OpenEXR/ImfInputFile.h>

Which form is actually intended to be used?

As an illustration, assume that I have a selected version of the headers 
available like this:

/libraries/OpenEXR/N.N.N/include/ImfInputFile.h

So I build using -I/libraries/OpenEXR/N.N.N/include with the expectation 
that that the former #include form is used.  However, if the source code 
uses the latter #include form, the code can end up picking up a 
different version of the headers such as the version that is provided 
with the Linux distribution, such as:

/usr/include/OpenEXR/ImfInputFile.h

There are various ways that I can address this.  One is to do make my 
selected version of the headers available like this:

/libraries/OpenEXR/N.N.N/include/OpenEXR/ImfInputFile.h

and then build using both -I/libraries/OpenEXR/N.N.N/include/OpenEXR and 
/libraries/OpenEXR/N.N.N/include to support both forms.

There are other approaches as well.

I suppose I will continue to need to support both forms since there is 
source out in the wild the uses both.

I guess I am curious about which form should be recommended.